Method and assembly for detecting the motion of an element

ABSTRACT

A method for detecting the motion of an element relative to a sensor apparatus is proposed, in which a detection of the direction of motion is performed. As a function of the direction of motion, a measurement signal is increased or decreased at predetermined measurement intervals, and only if a predetermined threshold value is exceeded is a direction-of-motion signal generated. Preferably, by means of a counting logic circuit ( 6 ), a counter is increased by a binary amount in one direction ( 2 ) and the counter ( 6 ) is decreased by a binary amount in the respective other direction ( 3 ). Upon a detection of measurement signals which as a result of being increased or decreased in a measurement interval do not lead to exceeding of the predetermined amount of the threshold value, vibration of the element is assumed.

PRIOR ART

The invention relates to a method and an apparatus for detecting themotion of an element relative to a sensor apparatus, in particular fordetecting the angle of rotation of a rotating element by way of asensor, in accordance with the preamble to the main claim.

Various embodiments of such sensor apparatuses are already in use, forinstance in vehicles. For instance with so-called Hall elements as rpmsensors on the wheels for an anti-lock brake system (ABS), as rpm andphase transducers for engine control, or as steering angle sensors forso-called vehicle dynamics control, and for electrical steering aids.

Among the most essential demands made of these rpm sensors, both in ABSand in the field of engines and transmissions, are as large an air gapas feasible and high immunity to vibration. However, it must be notedthat a highly sensitive sensor is intrinsically also highly sensitive toexcitation by the vibration that impairs the outcome of measurement andthat briefly also causes changes in the directions of rotation.

From German Patent Disclosure DE 197 50 304 A1, for instance, anapparatus for contactless detection of an angle of rotation by means ofa pulse wheel is known, in which direction of rotation detection ispossible by providing that in one direction of rotation, a change in thespacing of the pulse-tripping elements has been made, thus changing theduty factor.

To minimize the sensitivity of such sensor apparatuses to vibration, inconventional rpm sensors, a variable hysteresis is often also employed.This requires that first the signal amplitudes be measured, and thehysteresis is then adapted flexibly to them. For large input signals,major hysteresis is then selected, while a correspondingly reducedhysteresis is selected for small input signals; that is, when the airgap is small, the amplitude required for switching is increased. Asubstantial disadvantage of this method is the loss of immunity to airgap impacts during operation, which can briefly cause a major reductionin the signal amplitude. A previously increased hysteresis at theswitching point of the sensor, signal loss can then occur in the eventof an air gap impact.

Moreover, this method can be employed only once calibration of thesensor has been done, since it is only after calibration that the signalamplitude is known. Immediately after the sensor is switched on, thevibration sensitivity is still unchanged.

From U.S. Pat. No. 5,451,891, it is for instance known to use anadaptive hysteresis that is dependent on the signal amplitude. In thiscase, a coupling factor is determined, as a quotient of the measuredsensor amplitude and the frequency, and based on this coupling factor,the hysteresis is adjusted in proportion to the production of thecoupling factor and the frequency. With this known method, only thebehavior of passive sensors can be compensated for; such sensors furnisha very small signal for low excitation frequencies, and output a veryhigh amplitude for high frequencies. However, the behavior of sensorsthat regardless of the signal frequency furnish a constant internalsignal amplitude cannot be improved.

ADVANTAGES OF THE INVENTION

In a refinement of a method for detecting the motion of an element, inparticular for detecting the direction of rotation of a rotatableelement, relative to a sensor apparatus, with a detection of thedirection of the motion, advantageously, as a function of the directionof motion, a measurement signal is increased or decreased atpredetermined measurement intervals. Not until a predetermined thresholdvalue is exceeded is a direction signal, preferably adirection-of-rotation signal, then generated.

In a simple way, by means of a counting logic circuit, a counter canthen be increased by a binary amount in one direction, and the countercan be decreased by a binary amount in the other direction. Upon adetection of measurement signals which as a result of being increased ordecreased in a measurement interval do not lead to exceeding of thepredetermined amount of the threshold value, it can then be assumed thatthe element is vibrating.

A sensor apparatus which functions in accordance with the invention as arule already has integrated detection of the direction of rotation, asis already the case for modern rpm sensors, such as so-calleddifferential Hall sensors. Alternatively, however, other sensortechnologies may be employed, such as so-called magnetoresistive oroptical rpm sensors.

Detecting the direction of rotation is advantageously utilized accordingto the invention to make it possible simply and quickly to distinguishunambiguously between vibration and a genuine rotary motion. Unlike arotary motion with measurement pulses in an unambiguous direction ofrotation (such as left, left, left, et seq.), a rotary oscillation of atransducer wheel of the sensor apparatus is characterized by analternating direction of rotation (such as right, left, right, left, etseq.).

Detecting vibration is achieved by the invention for instance byintegration of the additional counter that has a sign, and this counteris incremented or decremented as a function of the value of the value ofa direction of rotation bit. The output of a rpm sensor of this kind canbe varied by the counter in such a way that the output is switched offas long as no unambiguous direction of rotation is detected, or in otherwords as long as the amount (without a sign preceding it) of the counteris below a threshold value which, depending on the desired immunity tovibration, is greater than or equal to two.

The above-described way of evaluating the preferabledirection-of-rotation signal makes it possible in a simple way to detectvibration of a transducer wheel in the form of angular vibration andthus to improve the immunity of the sensor apparatus, without thenecessity of increasing the hysteresis and thus worsening the resistanceto major signal fluctuations.

In addition, however, the possibility also exists of using the methoddescribed in addition to a variable hysteresis, to achieve furtherimprovement in the insensitivity to vibration. This is especially truefor applications in which the mechanical structure already prevents theoccurrence air gap impacts.

DRAWING

One exemplary embodiment of the invention will be described inconjunction with the drawing. Shown are:

FIG. 1, a flow chart of a method for detecting the rotary motion of atransducer wheel relative to a sensor apparatus, with detection of thedirection of rotation and with a counting logic component; and

FIG. 2, a graph of the counting values of the counting logic componentof FIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

In FIG. 1, a flow chart is shown for a method for detecting the rotarymotion of a transducer wheel, which in principle is known from the priorart, for instance for generating pulses for predetermined angles ofrotation, relative to a sensor apparatus. In block 1, a direction ofrotation detection circuit is represented symbolically; in block 2, thiscircuit generates a signal for the rotary motion “left”, and in block 3it generates a signal for the rotary motion “right”.

In the exemplary embodiment of the invention described here, a binarycounter state is increased by “1” in block 4 upon the detection of aleftward rotation, and decreased by “1” in block 5 upon detection of arightward rotation. In a counting logic component 6, the respectivecounter state is ascertained and evaluated for a sensor output 7, aswill be explained in conjunction with a graph shown in FIG. 2.

FIG. 2 shows the course of the counter state in the counting logiccomponent 6 over a measurement time t. The course of the counter state nover the time t, in the left-hand part of FIG. 2, shows the signature ofa vibration 8 a, which as a result of the change in direction ofrotation initially fluctuates relatively often between 0 and +1 andbriefly even extends to −1 and is thus within a threshold value of ±2.Within this range, vibration is thus detected, and the signal output 7is switched off (“output off”) on the basis of the condition: (amount(counter)<n, where n>1).

The course of the counter state n in the right-hand part of FIG. 2,conversely, shows an unambiguous direction-of-rotation signal 8 b, whichhere ranges from −1 across the threshold value ±2 to +1 and is thusoutside the threshold value of ±2. Within this range, no vibration isthus detected, and the signal output is thus switched on (“output on”)on the basis of the condition: (amount (counter≧n, where n>1).

The detection of the direction of rotation shown in blocks 1 through 3of FIG. 1 is thus advantageously utilized to generate an unambiguoussensor output signal 7 (“output on”; “output off”), which makes itpossible to distinguish between vibration, in the left-hand part of thegraph in FIG. 2, and a genuine rotary motion, in the right-hand part ofthe graph in FIG. 2.

1. A method for detecting the motion of an element relative to a sensorapparatus, having a detection of the direction of the motion,characterized in that as a function of the direction of motion, ameasurement signal is increased or decreased at predeterminedmeasurement intervals; and that not until a predetermined thresholdvalue is exceeded is a direction-of-motion signal generated:
 2. Themethod of claim 1, characterized in that by means of a counting logiccircuit (6), a counter is increased by a binary amount in one direction(2), and in the other direction (3) the counter (6) is decreased by abinary amount; and that upon a detection of measurement signals which asa result of being increased or decreased in the measurement interval donot lead to exceeding of the predetermined amount of the thresholdvalue, vibration of the element is detected.
 3. The method of claim 1characterized in that upon a detection of the measurement signals, fordetecting the motion of the element, a variable hysteresis isadditionally provided.
 4. The method of claim 1, characterized in thatfor detecting the motion of a rotatable element, the direction ofrotation is detected.
 5. A sensor apparatus for performing a method ofclaim 1, characterized in that the sensor apparatus has contactlesssensors, with which binary counting pulses (±1) can be generated atpredetermined motion intervals; and that an evaluation circuit includesa counting logic component (6), with which the counting pulses (±1) arecountable, and if the predetermined amount is exceeded, a directionsignal (7) can be generated, and otherwise, vibration of the element isdetectable.
 6. The sensor apparatus of claim 5, characterized in thatthe sensors include Hall elements.
 7. The sensor apparatus of claim 5,characterized in that the sensor apparatus is used as a rpm sensor in amotor vehicle.